U.S. Pat. Nos. 3,600,528, 3,643,041, 3,467,923, and 3,697,711 describe keyboards or switches having a movable contact member that is an integral part of a planar supporting substrate. Formerly, a plurality of discrete components, i.e., plungers and springs, were united to form a relatively complex electro-mechanical linkage. In the former structures the alleged advantages of the structures described in the patents are that they can be manufactured cheaply, with reduced tedium to the assembling personnel, and that they are more reliable.
In a copending United States Patent application, filed concurrently herewith by the inventor of the present invention and entitled "Switching Device and Keyboard," there is described a novel movable switching element which may be an integral part of a keyboard device using a plurality of such switching elements. The novel switching element is characterized by a set of unconnected, curved slots or apertures radiating outwardly from a central key area of a planar, metallic surface or substrate. The radially extending, unconnecting slots can be sections of a spiral, at least some of which overlap each other. In a preferred form of the switching element, the slots are involutes of a circle which are equally spaced around the central key areas. The slots provide a movable switching element that is strong and very easy to produce, thereby providing an improved switching device. Further, when depressed, the central key area of the switching element rotates, due to the action of the slots, such that a wiping contact with a fixed contact member is achieved with the resulting improved electrical properties
The aforementioned patent application teaches that the force-displacement characteristics of the movable switching element can be changed by adjusting the length or inner terminus of the radial extending slots. However, even with these adjustments, a structure with movable switching elements having a home position that is on the same plane with the remainder of the metal layer or substrate in, or from which, the switching elements are formed provides only a satisfactory mechanical sensory feedback signal through the fingertips of the operator. When depressing the switching elements, as through keys, it is best that the operator have a sufficient sensory feedback signal such that the operator can tell when a key has been depressed sufficiently to produce the desired electrical switching action. It is not desirable that the operator know that the switching has occurred through, or by means of, a hard stop action.